A study on photodegradation of polymers catalyzed by semiconductor

本研究分为两个部分：（1）固体高分子（聚氯乙烯PVC）和水溶性高分子（PEG和PVA）的光氧化;（2）生物高分子（如DNA、RNA、碱基和聚氨基酸）的光氧化。(1)在紫外光照射和/或太阳光照射下，研究了二氧化钛或氧化锌悬浮液中PVC固体颗粒和PVC薄膜的光催化氧化分解。监测二氧化碳的脱氯和释放，后者是通过乙酸和甲酸的中间作用发生的。在TiO_2-水介质中，添加过氧化氢和过硫酸钾等氧化剂，可促进聚合物试样的光降解。这些颗粒的光腐蚀也通过扫描电子显微镜检查。水溶性聚合物PEG和PVA也可通过羟基和/或醛类光降解为CH 3COOH、HCOOH和CO2气体。(2)本文研究了在UV-A和UV-B辐射下，在物理防晒剂TiO_2/金红石微粒存在下，DNA和RNA的敏化光化学反应，以评估这种物理防晒剂与这些底物接触时可能引起的损伤。这两种核苷酸部分分解为二氧化碳，氮转化为氨和硝酸根离子。通过透射电镜、扫描电镜、凝胶渗透色谱等手段证实了对DNA的物理和化学损伤。此外，氮在各种氨基酸中的去向也作为基础研究进行了检查。氨基酸中的氮主要被光转化为NH_4^+，少量转化为NO_3^-离子。

The research is composed of two sections ; (1) Photooxidation of solid polymers (polyvinylchloride PVC) and water-soluble polymers (PEG and PVA) (2) Photooxidation of biopolymers such as DNA,RNA,bases and polyamino acids.(1) The photocatalyzed oxidative decompositions of solid particles of PVC and a PVC film have been examined in suspensions of titania or zinc oxide illuminated by UV light and/or by solar exposure. Dechlorination and evolution of carbon dioxide were monitored, the latter occurring by the intermediacy of acetic and formic acids. The photodegradation of polymer specimens was enhanced in TiO_2-water media by such added oxidants as hydrogen peroxide and potassium persulfate. Photocorrosion of these particulates was also examined by scanning electron microscopy. Water-soluble polymers of PEG and PVA were also photodegraded to CH_3COOH,HCOOH and CO_2 gas via hydroxyl and/or aldehydes.(2) The sensitized photochemistry of DNA and RNA has been examined under UV-A and UV-B radiation in the presence of a physical sunscreen agent, TiO_2 anatase/rutile particles, to assess the possible damage that such an agent might cause on contact with such substrates. These two nucleotides are partially decomposed to carbon dioxide and the nitrogen are converted to ammonia and nitrate ions. The physical and chemical damage done to DNA was confirmed by TEM and SEM,and gel permeation chromatography. In addition, the fate of nitrogen in various amino acids was also examined as a fundamental research. The nitrogen in the amino acids are photoconverted predominantly into NH_4^+ and to a lesser extent into NO_3^- ions.